24.
The perimeter of a rectangle l × w is P = 2l + 2w.
We have l = 3x² - 2y² and w = x² + 3xy. Substitute:
P = 2(3x² - 2y²) + 2(x² + 3xy) use distributive property
P = (2)(3x²) + (2)(-2y²) + (2)(x²) + (2)(3xy)
P = 6x² - 4y² + 2x² + 6xy combine like terms
P = 8x² + 6xy - 4y²